Pneumocystis carinii is a major pathogen of patients with HIV infection. The immune responses to P. carinii are poorly understood, but cytokines may play a role in both clearing P. carinii infection and in the hypoxia associated with P. carinii pneumonia that may be exacerbated following initiation of therapy. To investigate which cytokines are being activated during P. carinii pneumonia, collaborative studies have been undertaken with investigators at Indiana University and LPD, NIAID. At Indiana, lungs were harvested at various timepoints from mice inoculated with P. carinii that have been immunosuppressed by administration of an anti-CD4 monoclonal antibody that eliminates CD4 cells. Immunosuppression is either maintained or discontinued, or animals are treated with TMP-SMX to clear the P. carinii pneumonia. Three animals per group are utilized, and a portion of the lung is scored for P. carinii infection. The remainder is processed by our group for RT-PCR, using primers specific for a large number of cytokines, including IL-1beta, TNF, lL-2, IL-4, lL-5, IL-6, IL- 10, IL-12, and gamma interferon. Collaborating LPD investigators have used this technique and methodology in previous studies with other pathogens. This PCR technique allows semiquantitation of the amount of message present in the lung for the indicated cytokines. Preliminary results suggest that IL-10 and possibly gamma interferon, are increased during PCP. It is hoped that these studies will provide insights into the role of cytokines in P. carinii pneumonia, and may provide mechanisms for increasing clearance or decreasing the inflammation that may be causing hypoxia.